Is THIS even at all possible??

Hi all, I've got a quick few questions. First off I just received some logitech z560's to replace my FPS 2000. The 560's are a definite improvement although my FPS 2000 served me very well and I still consider to be a great speaker system. Rather than relegate these to the back of the dusty closet, I got to thinking one day and started to wonder whether it would be possible to connect BOTH the FPS 2000 and the z560's to my SB Live X-gamer.
As you know the SB live has a digital out which I connect my FPS 2000's to, which still leaves the rear out and the line out jacks open on the back of the card (and this is of course where the z560's connect to)
I don't claim that this is reasonable and have no trouble admitting to the ridiculous nature of this question, but would it be possible to run both speaker setups off of the single card simultaneously without damage to either the speakers or sound card?? I have absolutely no idea what I am dealing with here and so I haven't had the courage to try it yet, until I receive some educated advice. My thanks goes out to all those that take the time to offer their advice!

P.S. One last one. Given that I primarily listen to MP3's, from those who have personal experience with this issue, will I notice a sound difference between the Live X-gamer and the new Audigy to justify spending the money on the upgrade??

Thanks once again for your guidance!